1. Field of the Invention
This invention relates to a perpendicular magnetic recording apparatus and a perpendicular magnetic reproducing apparatus.
2. Description of the Related Art
In the field of magnetic recording, perpendicular magnetic recording is advantageous in increasing the recording density and decreasing the wavelength.
Moreover, the perpendicular magnetic recording medium for this perpendicular magnetic recording must have a high coercive force and high residual magnetic flux density. Various researches and developments have been made for the requirements. Some typical perpendicular magnetic recording rigid disks are already proposed of which the perpendicular magnetic recording layers are all made of CoCr alloy.
However, since the saturation magnetic flux density 4.pi.Ms of this CoCr alloy is as small as 4 to 6 kG (kilogauss), the reproduced output proportional thereto is less than the practical level. Particularly, because of the characteristic of the perpendicular magnetic recording, the reproduced output of a long wavelength (.lambda.&gt;1 .mu.m) range is much less than that of the widely used elongated-type magnetic recording medium.
In addition, although the reproduced output tends to increase with the increase of the coercive force of the CoCr layer, the magnetic head for perpendicular magnetic recording, particularly a single-pole magnetic head, has a low head efficiency. Also, the available soft magnetic core materials for the magnetic head have insufficient saturation magnetic flux densities. Therefore, the endeavor to increase the coercive force of the CoCr layer is not effective.
Of course, the coercive force itself of the CoCr alloy thin film has a limit, or at most 1500 (Oe).
Furthermore, although the index of recording density, D.sub.50 (the recording density at which the output is halved relative to the long-wavelength output) increases with the increase of the anisotropic magnetic field in the magnetic layer, this index of CoCr alloy is limited to at most 4 to 6 kOe.
The vertical coercive force Hcv of the CoCr-based alloy is 1500 (Oe) as given above when the base on which this alloy is deposited by sputtering or the like is heated to about 150.degree. C., but it is as low as about 300 (Oe) when the base temperature is equal to about the room temperature. The vertical square ratio (Mr/Ms) is about 0.2. In this case, the saturation magnetic flux density Bs is relatively low, and the base temperature for deposition must be kept high in order for the vertical coercive force Hcv to be increased. Therefore, the disk base to be used must have a high heat-resistance. The necessity for high base temperature will incur various industrial disadvantages.
To cope with this problem, the assignee of the present application has previously proposed a CoPt-group-based material, or a CoPt-chiefly-containing perpendicular magnetic film in Japanese Laid-Open Patent Publication Nos. 2-74012, No. 2-74013 and No.2-73510. This CoPt-group-based perpendicular magnetic film has a sufficiently large coercive force Hc even when the film thickness is increased to be large enough. In addition, the disk base temperature thereof is not necessary to be increased upon deposition, and the saturation magnetic flux density Bs is sufficiently large.
However, when the conventional magnetic head is used for recording and reproducing this kind of CoPt-group-based perpendicular magnetic film, high-density recording and high-output reproduction cannot be performed even by making effective use of the characteristics of this film.